JSON parsing

Parser.scala

import scala.util.parsing.json.JSON

case class Widget(name: String, flavour: String)
case class Contract(vendor: String, colour: String, widgets: List[Widget])

object Parser {

  def parseContract(json: String): Option[Contract] = {
    for {
      AsMap(contract) <- JSON.parseFull(json)
      AsString(vendor) <- contract.get("vendor")
      AsString(colour) <- contract.get("colour").orElse(Some("None"))
      AsList(widgets) <- contract.get("widgets")
    } yield {
      Contract(vendor, colour, for {
        AsMap(widget) <- widgets
        AsString(name) <- widget.get("name")
        AsString(flavour) <- widget.get("flavour").orElse(Some("Strawberry"))
      } yield Widget(name, flavour))
    }
  }
}

/*
 * Some extractors to avoid boilerplate and casting
 */
object AsList {
  def unapply(list: List[Any]): Option[List[Any]] = Some(list)
}

object AsMap {
  def unapply(map: Map[String, Any]) = Some(map)
}

object AsString {
  def unapply(str: String) = Some(str)
}

object Test {
  val json = """
{
  "vendor"  : "Whoever",
  "colour"  : "blue",
  "widgets" :            
  [
    {
      "name"    : "One",   
      "flavour" : "Lime"   
    },
    {
      "name"    : "Two",   
      "flavour" : "Banana"
    },
    {
      "name"    : "Three"   
    }
  ]
}"""

  def main(args: Array[String]) {
    println(JSON.parseFull(json))
    println(Parser.parseContract(json))
  }
}